Stabilized methyl chloroform

ABSTRACT

The tendency for methyl chloroform to decompose in the presence of metals, particularly aluminum, is inhibited by a stabilizer mixture comprising an epoxide, a nitroalkane, trioxane and either propylene glycol mono-methyl ether, dioxepane or a mixture thereof.

REFERENCE TO A CO-PENDING APPLICATION

This is a division of application Ser. No. 243,072 filed Apr. 11, 1972,now U.S. Pat. No. 3,864,413, which is in turn a continuation-in-part ofapplication Ser. No. 5,101 filed Jan. 22, 1970, and now abandoned.

BACKGROUND OF THE INVENTION

The usefulness of various chlorinated lower aliphatic hydrocarbons,particularly for the liquid and/or vapor phase degreasing of metals, isby now well known. Besides their excellent cleaning properties, thesechlorinated solvents are well suited for industrial use owing to theirlack of flammability and relatively low cost. The most widely used ofthese solvents are carbon tetrachloride, trichloroethylene,perchloroethylene and methyl chloroform (1,1,1-trichloroethane). Ofparticular interest from this group is methyl chloroform, the excellentsolvency and low toxicity of which make it particularly suitable for theindustrial cleaning (degreasing) of metals.

A problem in the commercialization of methyl chloroform has arisen,however, owing to its pronounced tendency to decompose in the presenceof a number of metals, especially aluminum. Thus, while others of thechlorinated solvents, such as perchloroethylene, must be stabilizedagainst decomposition induced by a wide variety of factors, the problemis nowhere near as marked as in the case of methyl chloroform, which, ifexposed unprotected to aluminum, will be rendered useless within amatter of minutes.

Thus it will be apparent, and indeed research has shown, that whileother chlorinated solvents may be stabilized through the use of smallquantities of a wide variety of substances, the compounds capable ofstabilizing methyl chloroform against metal-induced decomposition arequite limited in number and generally must be used in comparativelylarge amounts. Obviously, the requirements being strict and theselection limited, a number of problems have arisen in attempting toperfect a stabilizer system which will protect methyl chloroform and themetals being treated therewith against decomposition in both the liquidand vapor phases in the presence of a wide variety of contaminants.First, relatively large quantities being required, the stabilizers mustbe economically practical. Further, while the problems of liquid phasestabilization are often different from those of vapor phasestabilization and hence different stabilizers will be useful, the methylchloroform may be used interchangeably for both liquid and vapordegreasing applications and therefore the components must be compatibleover a wide range of temperatures.

While generalizations are indeed difficult with respect to thestabilization of methyl chloroform, it may be safely stated that many ofthe stabilizer systems used commercially and set forth in the patentliterature describe and feature the use of nitroalkanes and epoxides.Although it is true that many stabilizer systems are "built" from thisnitroalkane-epoxide base, the combination itself is not alwayscompletely effective for the stabilization of methyl chloroform and itis the selection of the remaining components of any system whichdetermines its ultimate success or failure.

STATEMENT OF THE INVENTION

Therefore, it is an object of the present invention to provide amulti-component stabilizer system for the inhibition of thedecomposition of methyl chloroform, particularly when used as a solventfor the liquid and vapor phase degreasing of metals.

It is a further object of the present invention to improve upon and makecommercially practical a stabilizer system for methyl chloroform basedupon a nitroalkane-epoxide combination.

These and further objects of the present invention will become apparentto those skilled in the art from the description and claims whichfollow.

It has now been found that a composition particularly suitable for metaldegreasing applications comprises methyl chloroform together with astabilizing amount of a mixture of 1) a nitroalkane, 2) an epoxide, 3)trioxane and 4) an additive compound selected from the group consistingof propylene glycol mono-methyl ether and dioxepane. The effectivenessof this composition is enhanced by the additional presence of an alcoholselected from the group consisting of methyl butynol and t-amyl alcohol,and, when such an alcohol is used, a hydrocarbon may be added withfurther beneficial effect. Optimum compositions for certain degreasingapplications also include an alkaline compound. Such compositions andvariations thereof are readily adaptable to the varied requirements ofthe metal degreasing field and may also be used in any other applicationwhere a stabilized grade of methyl chloroform is required.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The term "nitroalkane," as used in the specification and claims, isintended to refer to those nitro-aliphatic compounds generally used inthe stabilization of chlorinated solvents, preferably those containingfrom 1-3 carbon atoms. Included are nitromethane, nitroethane,1-nitropropane and 2-nitropropane.

The definition of the term "epoxide" is also that commonly used in thechlorinated solvents art and is intended to especially refer toaliphatic epoxides substituted or unsubstituted, containing from 3-8carbon atoms. A primary consideration is that the boiling point of theepoxide compound does not differ substantially from that of methylchloroform. Illustrative of the preferred epoxides are butylene oxide,propylene oxide, epichlorohydrin and methyl glycidyl ether.

The term "hydrocarbon" refers to a wide variety of materials such asstraight chain or cyclic aliphatics, both saturated and unsaturated, aswell as aromatics. Examples of such hydrocarbons useful in the inventionare; hexane, heptane, octane, hexene, trimethyl pentene, cyclopentane,cyclohexane, cyclohexene, cyclooctene, toluene and the like. Many otherhydrocarbons will also be useful depending upon, primarily, theirboiling points and economics, with a wider variety obviously beinguseful for cold degreasing applications.

The use of the term "alkaline compound" in referring to the optimumcompositions of the present invention is intended to include both thosecompounds which are alkaline per se, e.g., amines, and so calledalkaline precursors, e.g., oximes or hydrazones. The alkaline compoundsuseful are those soluble in methyl chloroform and generally have boilingpoints substantially corresponding to methyl chloroform. It is apparent,however, that certain of these alkaline compounds form azeotropes withthe methyl chloroform and/or other components of the stabilizer systemthus altering their apparent boiling points. Those alkaline compoundsespecially preferred at this time include N-methyl morpholine,diisopropylamine and pyrrolidine.

It should be understood that the term "dioxepane" is used in the genericsense to include both 1,3- and 1,4-dioxepane. The 1,3 isomer is mostcommon and hence preferred. However, it may be "contaminated" with orreplaced by the 1,4 material without evident change.

The apparent purpose of both trioxane and propylene glycol mono-methylether and/or dioxepane is to act as an extender for thenitroalkane-epoxide base. However, it has been found that trioxane,while effective and economically desirable, cannot be incorporated intomethyl chloroform in sufficient amounts, owing to its tendency onboiling to concentrate in the sump and crystallize from solution, to beeffective. Further additions of propylene glycol mono-methyl etherand/or dioxepane, however, provide the necessary stabilization to renderthe system both effective and practical. The invention is thus mostuseful in the usual instance where large amounts of stabilizers must bepresent.

While the combination of methyl chloroform with a nitroalkane, anepoxide, trioxane and an additive compound selected from the groupconsisting of propylene glycol mono-methyl ether and dioxepane is quiteeffective for most applications it has been found that the effectivenessof the stabilizer system, especially its ability to resist aluminumattack at ambient temperatures upon dilution, is improved by theaddition of an alcohol selected from the group consisting of t-amylalcohol and methyl butynol. This function is considered important sincea commercial product should be able to withstand considerable dilutionwithout any substantial loss in effectiveness. This requirement is metby either t-amyl alcohol, methyl butynol, or mixtures thereof, withoutthe problem usually inherent in the use of most alcohols for thestabilization of methyl chloroform solutions when used for vapor phasedegreasing. Particularly, this problem relates to the fact that, whileseveral alcohols are found to be effective at ambient temperatures incold degreasing applications, these alcohols often detrimentally affectsteel or aluminum surfaces in contact therewith at reflux temperatures.The disclosed alcohols have been found to be uniquely effective.

The use of the alcohols just mentioned is rendered even more effectivefor dilution control, and the distillation range of the stabilizedsolvent is improved, by the additional presence of a hydrocarbon, forexample, heptane. The economic advantage of such a relativelyinexpensive material is readily apparent when it is realized that thepresence of a hydrocarbon may allow a reduction in quantity of theother, more expensive, components.

Where the corrosion of steel in the presence of methyl chloroform in thevapor phase is a problem, it may be desirable to add one of the manyalkaline compounds known to be useful for this purpose. One or more ofthese alkaline compounds may be added to the compositions of the presentinvention in the presence of the alcohol, a hydrocarbon, both orneither, as the requirements of the system dictate.

Generally the amount of the stabilizing mixture added to the methylchloroform will be that required to effect stabilization, economically,over a wide range of conditions, which amount will vary according to theapplication. It is usually found, however, that the composition willinclude from 90-99 percent by weight of methyl chloroform and from 10-1percent by weight of the stabilizer mixture. Preferably from 4-6 percentof the composition will consist of the stabilizing components.

Referring to the stabilizers themselves, they may be present in thetotal stabilized system in amounts, expressed in percents by weight, asfollow: 0.1 to 2.0 nitroalkane; 0.05 to 0.5 epoxide; 0.1-1.0 trioxane;0.1 to 2.0 propylene glycol mono-methyl ether and/or dioxepane; 0.1 to2.0 t-amyl alcohol and/or methyl butynol; 0.1 to 2.0 hydrocarbon, and0.001 to 0.1 alkaline compound.

In order that those skilled in the art may more readily understand andappreciate the present invention, the following specific examples areafforded. In these examples a number of tests are referred to and areused to evaluate the effectiveness of the various stabilizer systems.

The "aluminum scratch test" consists of immersing a section of aluminummetal in the methyl chloroform solution to be evaluated and scratchingthe immersed surface with a fine-pointed stylus in order to present afresh surface to the solvent. The test, which is strictly qualitative innature, is effective as a screening method since, obviously, if thestabilized methyl chloroform system cannot pass this simple test, itwill not stand up to the more rigorous tests which follow. Evidence offailure is represented by "bleeding", i.e., continuous discoloration ofthe solvent, at the point of the scratch.

A further and more rigorous test applied to systems which pass thescratch test is the "72 hour aluminum reflux test". In this test 100milliliters of the solvent system and 0.2 milliliter of water are placedin a flat-bottomed flask fitted with a condenser. Two strips of aluminumare inserted, one in the liquid in the flask (pot), the other hung inthe condenser where the solvent vapor during the extended period ofgentle reflux surrounds, condenses on, and drips from, the strip. Againthe test is mainly qualitative in nature and poor results are readilyevidenced by corrosion of the aluminum and discoloration of the solvent.A further use of this test is to determine the acid content of thestabilized solvent by measurement of the final pH. Unless otherwisestated, all systems have an initial pH of 7 or above. Upon completion ofthe 72 hour reflux test, the solvent is cooled and extracted in a 1:1ratio with neutral water, the pH of the aqueous phase being subsequentlydetermined. A low pH is of course indicative of the presence of acidliberated by the decomposition of the solvent and serves as anindication of the effectiveness of the stabilized system in preventingcorrosion of the aluminum and decomposition of the solvent.

EXAMPLE 1

The Table, hereinbelow, compares the effectivness of the variousmulti-component compositions of the present invention and is for themost part self-explanatory.

                                      TABLE                                       __________________________________________________________________________                   Total  A1*                                                                    Wt.    Scratch                                                                            72 Hr. A1 Reflux Test                              Stabilizer System                                                                            Stabilizers                                                                          Test Pot**                                                                             Condenser**                                                                          pH                                      __________________________________________________________________________    1.                                                                              Nitroethane                                                                            3.6%                                                                 Butylene oxide                                                                         0.4%                                                                              4.0    3    --  --     --                                      2.                                                                              Propylene glycol                                                              mono-methyl                                                                   ether (PGME)                                                                           2.8%                                                                              2.8    2    --  --     --                                      3.                                                                              Nitroethane                                                                            0.8%                                                                 Butylene oxide                                                                         0.4%                                                                 Trioxane 2.8%                                                                              4.0    1    A***                                                                              C      4.5                                     4.                                                                              Nitroethane                                                                            0.8%                                                                 Butylene oxide                                                                         0.4%                                                                 PGME     2.0%                                                                 Trioxane 0.8%                                                                              4.0    1    A   C      6.0                                     5.                                                                              Nitroethane                                                                            0.8%                                                                 Butylene oxide                                                                         0.4%                                                                 1,3-Dioxepane                                                                          1.8%                                                                 Trioxane 1.0%                                                                              4.0    1    A   B/C    4.4                                     6.                                                                              Nitroethane                                                                            0.8%                                                                 Butylene oxide                                                                         0.4%                                                                 1,3-Dioxepane                                                                          1.0%                                                                 PGME     0.8%                                                                 Trioxane 1.0%                                                                              4.0    1    A   B      5.4                                     7.                                                                              Nitroethane                                                                            0.8%                                                                 Butylene oxide                                                                         0.4%                                                                 PGME     2.0%                                                                 Trioxane 0.8%                                                                 Methyl butynol                                                                         1.0%                                                                              5.0    1    A   A      6.7                                     8.                                                                              Nitroethane                                                                            0.8%                                                                 Butylene oxide                                                                         0.4%                                                                 PGME     1.0%                                                                 Trioxane 0.6%                                                                 t-Amyl alcohol                                                                         1.5%                                                                              4.3    1    A   B      7.0                                     __________________________________________________________________________     Note:                                                                          *1 = no effect, 2 = pinholes but heals, 3 = continuous bleeding               **A = no corrosion, B = slight corrosion, C = severe corrosion               *** Trioxane crystals observed in pot on solvent loss.                   

It will be seen from the Table that the combination of nitroethane andbutylene oxide (Sample 1) fails the scratch test and hence isunacceptable as a stabilizer system for methyl chloroform. PGME (Sample2) also fails the scratch test. The addition of trioxane to Sample 1(Sample 3) improves scratch test results but leaves an unacceptableresidue on solvent loss simulating a vapor degreasing operation.However, as is shown by Samples 4, 5 and 6, the combination ofnitroethane, butylene oxide, trioxane and PGME and/or dioxepane resultsin a stabilized methyl chloroform composition which is entirely suitablefor use in cold degreasing applications as evidenced by the improvedresult on the aluminum scratch test and which leaves no unacceptable pot(sump) residue on distillation. Samples 7 and 8 show that the furtheraddition of methyl butynol or t-amyl alcohol significantly improves thestabilized methyl chloroform system of Sample 4 to the effect that goodto excellent results are obtained, under conditions simulating vapordegreasing applications, according to the 72 hour aluminum reflux test.

EXAMPLE 2

A methyl chloroform solution stabilized with 0.4% butylene oxide, 1.8%propylene glycol mono-methyl ether, 1.0% trioxane and 0.4% nitromethanegives excellent results on the aluminum scratch test. After the 72 houraluminum reflux test, a final pH of 6.9 is obtained and the condenserstrip is only slightly stained while the solvent remains water-white andclear.

EXAMPLE 3

A methyl chloroform solution stabilized with 0.4% butylene oxide, 1.0%propylene glycol mono-methyl ether, 0.5% trioxane, 1.5% t-amyl alcohol,0.8% nitroethane, 1.5% heptane and 0.02% N-methyl morpholine givesexcellent results on the aluminum scratch test. After the 72 houraluminum reflux test, the condenser strip shows only a slight stain andthe pH after the test is 7.6 while the solvent remains water-white andclear.

While the invention has been described with reference to certainspecific and preferred embodiments thereof, it is not to be so limitedsince certain alterations may be made which are still within the scopeof the appended claims.

What is claimed:
 1. A stabilized composition which consists essentially of methyl chloroform containinga. 0.1 to 2.0 percent by weight of a nitroalkane of from 1 to 3 carbon atoms. b. 0.05 to 0.5 percent by weight of an aliphatic epoxide selected from the group consisting of propylene oxide, butylene oxide, epichlorohydrin and methyl glycidyl ether, c. 0.1 to 1.0 percent by weight of trioxane, and d. 0.1 to 2.0 percent by weight of propylene glycol monomethyl ether.
 2. The composition of claim 1 wherein the nitroalkane is nitromethane and the aliphatic epoxide is butylene oxide.
 3. The composition of claim 1 wherein the nitroalkane is nitroethane and the aliphatic epoxide is butylene oxide. 